268 On the Combinations of the yellow Oxide of Lead 
instead of being precipitated in yellow scales, it takes the form 
of pale-red needles which unite in stars. As this salt is only 
formed after the yellow salt, and with a greater quantity of lead 
than that which served to form the latter, it is evident that it 
ought to contain more base, and that it ought to be regarded as 
asubnitrite. Before explaining the properties of these two salts, 
I shall premise that it is very difficult (perhaps even impossible) 
to obtain perfectly pure nitrite by M. Proust’s process: in fact, 
if we have not boiled the acid nitrate long enough over the lead, 
the nitrite may contain nitrate. Finally, if the ebullition has 
been too long, the nitrite retains some subnitrite, as appears 
from its colour verging towards red. The best process for pre- 
paring the nitrite consists in passing a current of carbonic acid 
into the solution of subnitrite, and in evaporating the liquor se- 
parated from the carbonate of lead: We then obtain crystals of 
nitrite, which we must press between bibulous paper to dry them: 
afterwards they must be exposed to the sun. Almost all my ex- 
periments were made with nitrite of lead produced by the sub- 
nitrite. 
Examination of the Nitrite of Lead. 
15. It crystallizes in yellow leafy flakes. 
16. It is not very soluble in cold water: besides, its solution 
has but a slightly astringent and saccharine taste. 100 grammes 
of boiling water may dissolve about 9°41 gr. 100 parts of water 
at 23° of the centigrade thermometer, when mixed with 2 gr. of 
nitrite reduced into powder, dissolved 1-26 gr. after bemg 24 hours 
in contact. When we make a solution in boiling water, and - 
when we cool it to 23°, the water retains more nitrite than it 
would have dissolved at the same temperature. 
These determinations are not rigorous, because, when we dis- 
solve the nitrite in water, there is always a portion of it decom- 
posed by the carbonate of ammonia contained in the distilled 
water. 
It appears to me, that when we crystallize several times the 
nitrite (coming from the snbnitrite) the first crystals obtained 
from it contain more base than those which are formed alter- 
wards, and that the mother water of the latter was slightly acid. 
The first crystals were of a deeper yellow than the rest: they 
yielded when analysed one centieme of base more than the latter. 
17. The solution of nitrite is yellow, it brings back to blue 
turnsole paper which has been reddened by an acid: it does not 
perceptibly absorb oxygen gas, at least after a contact of three 
days ; when exposed to the air it is covered with a white pellicle 
of carbonate, 
18. The 
